The interlaminar and horizontal connectivity of the neocortex segregates its neuronal elements into local networks. The cellular mechanisms underlying cortical network activity, and the impact of local cortical network activity during sensory processing remain largely unknown. In vivo, neurons of the neocortex exhibit rhythmic, spontaneous cycles of synaptically mediated depolarization, termed UP states, followed by cessation of synaptic activity, termed DOWN states. This proposal will specifically examine the cellular basis and functional consequences of spontaneous, persistent activity during UP states in the mammalian neocortex in vivo. The first aim of this proposal will characterize the contributions of excitation and inhibition during the spontaneous network activity of the UP state. This will be accomplished via single and paired intracellular recording, simultaneous with extracellular unit and local field potential recordings in anesthetized ferret prefrontal cortex. The second aim of this proposal will assess the effect of this ongoing network activity upon visual responsiveness of neurons in cat visual cortex, using methods described above. The proposed plan will provide insights into the dynamic operation of intact neocortical circuits. [unreadable] [unreadable]